It seems obvious that our personality is handed down to us much like our older siblings’ clothes. But the question is, how is it handed down? Does it have a genetic basis, or is it shaped by our experiences and surroundings?
In a previous post, I discussed the two main ways researchers are approaching this question. Twin studies, the oldest method, seek to identify the heritability of a trait on the basis of observations of twins, including those separated at birth and reared apart (Bouchard et al., 1990).
Genetic testing is a newer way of gaining insight into a trait's heritability. In comparison, twin studies yield higher heritability estimates. But the estimates are still regarded as useful for stable traits (i.e., traits like height that don't undergo random or unsystematic changes). For stable traits, there is a neat correlation between twin studies and genetic studies: heritability estimates from genetic studies are about one half of the estimates from twin studies. Though in some research on personality traits, the estimates are even smaller.
Why do the data from twin studies paint such a different picture of heritability? As I hinted at previously, I think the larger twin-based estimates may be due to co-variation (or confounding, if you will)—not biological co-variation, but rather co-variation that came into existence as a result of human innovation (Brogaard, 2016, 2020).
Take basketball. Prior to its invention, you obviously couldn’t join a basketball team. So the attribute of having joined a basketball team isn't a product of natural selection. However, people who are tall and athletic are probably more likely to join a basketball team than people who are short and scrawny. So the attribute of having joined a basketball team isn’t a real phenotype with a genetic basis; it probably co-varies with highly heritable traits like being tall and athletically built. As twins with a tall stature and an athletic build are more likely to join a basketball team than twins who are short and scrawny, twin studies can make the attribute of having joined a basketball team look like it has a genetic basis.
Now, here is the idea I am going to run with: the data from twin studies suggest that extraversion, agreeableness, and conscientiousness (and/or their facets) have such a strong genetic basis in part because they co-vary with highly heritable traits such as size of cheekbones, location of eyebrows, and eye shape.
This suggestion may seem implausible at first. After all, how could aspects of your personality co-vary with physical attributes like the size of your cheekbones or the location of your eyebrows? Aren’t your personality and your facial appearance independent variables?
Well, probably not. In fact, there is evidence to suggest that prominent cheekbones and high inner eyebrows reliably signal trustworthiness, whereas other facial features reliably signal other facets of personality (Olivola et al., 2014).
Cues like prominent cheekbones and high inner eyebrows are thus very different from cues like laugh lines and clarity of eyes. If you smile a lot, this may mark your face in such a way that it looks like you are always smiling a little (think MSNBC news anchor Lawrence O’Donnell, weekdays 10 p.m. ET). But you don’t get prominent cheekbones from being trustworthy (Brogaard, 2016).
The upshot of my thinking is this: trustworthiness doesn’t cause prominent cheekbones and high inner eyebrows. Rather, facial features that reliably signal trustworthiness, such as higher brows and cheeks, are likely to shape the development of our adult personality. When your 11-year old looks up at you with his prominent cheekbones and high inner eyebrows, insisting he is old enough to stay home alone, he has already won you over with his brows and cheeks. But when your youngest turns 11, and he looks up at you with his low brows and round cheeks, insisting he is old enough to stay home alone, you automatically spot a lack of trustworthiness in his face and respond with a firm “no.”
Over time, your unreflective but differential reactions to your kids’ distinct physical appearances may influence the development of their adult personality. As most adults and some kids will react in similar ways, your kids’ interactions with others will probably only magnify the marks you left on their developing personalities.
You may have noticed a similarity between facial biases and racial biases, and rightly so. Our projections of different personality traits onto people with different looks are driven by unconscious biases, akin to our unconscious racial biases. As Olivola et al., (2014) point out, our automatic reactions to people’s brows and cheeks reveal our face-ism—the tendency we have to treat people with distinct facial appearances differently, even our own children. Of course, similar remarks apply to various bodily features.
Our biases against certain facial and bodily appearances could help explain why we are likely to become the kind of person people take us to be. This, in turn, may explain how our facial and bodily appearance could have a significant impact on our personality. As many of our facial and bodily features have a genetic basis, it’s not hard to see how a twin study could make it look as if the facets of personality that co-vary with physical appearance are largely rooted in our genes as well.
I suspect extraversion, agreeableness, and conscientiousness are the most “visible” among the Big Five, eliciting valid clues that are easy to recognize. For example, an energetic stance, stylish clothing, a strong gaze, a confident smile, and a healthy and attractive look have been shown to be valid cues for high extraversion (Albright et al., 1988).
Openness concerns our interest in more intellectual endeavors such as art, politics, and spirituality, and is therefore less likely to elicit highly visible (or other sensory) cues. (After all, not all of us are giving political speeches or preaching in a church, for example). I suspect that neuroticism, which shares a substantial number of genes with openness, also has fewer highly visible cues than extraversion, agreeableness, and conscientiousness do.
But if there are fewer easily noticeable cues to a personality trait, then this may prompt us to attribute the trait unreflectively. So, for the cases of openness and neuroticism, we may be less likely to get co-variation between personality and physical appearance. Of course, whether we in fact exercise more care before making judgments about openness and neuroticism is ultimately an empirical question.
Albright, L., Kenny, D. A., & Malloy, T. E. (1988). "Consensus in personality judgments at zero acquaintance." Journal of Personality and Social Psychology 55, 3: 387–395.
Bouchard, T. J., Jr; Lykken, D. T.; McGue, M.; Segal, N. L.; Tellegen, A. (1990) "Sources of Human Psychological Differences: The Minnesota Study of Twins Reared Apart." Science 250, 4978: 223.
Brogaard, B. (2020). Hatred: Understanding Our Most Dangerous Emotion, Oxford University Press.
Brogaard, B. (2016). "Perceptual Appearances of Personality." Philosophical Topics, 44, 2, New Directions in the Philosophy of Perception: 83-104.
Olivola, C. Y.; Funk, F.; Todorov, A. (2014). “Social Attributions from Faces Bias Human Choices,” Trends in Cognitive Sciences 18, 11: 566-70.
Power, R. A.; Pluess, M. (2015). "Heritability estimates of the Big Five personality traits based on common genetic variants." Transl Psychiatry 5, 7: e604. Published online 2015 Jul 14. doi: 10.1038/tp.2015.96